1. Field of Invention
This invention relates generally to disposable cups, specifically to an insulated paper cup.
2. Prior Art
There are three main types of disposable cups: paper, expanded resin, and polystyrene. Polystyrene cups are aesthetically pleasing, but they can only be used for holding cold drinks, and are not biodegradable or recyclable. Cups of expanded synthetic resin material, sold under the trademark Styrofoam, are excellent thermal insulators, so that they can maintain the temperature of a drink, whether hot or cold, for long periods of time. They are comfortable to handle because their exteriors stay close to ambient temperature, regardless of the temperature of the drink. However, they are environmentally unfriendly, because they are not biodegradable or recyclable. As a result, they are being banned from many municipalities.
Standard single-layer paper cups are recyclable, and therefore more environmentally sound. However, they are poor thermal insulators, so that a beverage in a paper cup quickly looses its cold or heat. They are also uncomfortable to handle, because a hot drink can burn a hand, whereas a cold drink will cause condensation on their outsides, making them slippery and difficult to hold. Their single-layer construction makes them fragile, so that large cups filled with liquid easily crumble after prolonged handling.
Multi-layered paper cups have been designed for providing thermal insulation and increased strength. U.S. Pat. Nos. 2,661,889 to Phinney (1948), 4,993,580 to Smith (1991), 5,092,485 to Lee (1992), and 5,205,473 to Coffin (1993) show three-layered cups with smooth outer and inner shells, and a corrugated middle layer. The corrugated layer provides air pockets for thermal insulation and added strength to withstand prolonged handling.
Although strong and thermally efficient, these cups are all expensive to manufacture, because their three layers are formed separately and then assembled together. This requires at least three glue joints for the forming the layers into tapered cylinders, two glue joints for assembling the layers together, and a glue joint for attaching the bottom. Some cups require even more glue joints. The liberal use of glue renders the cups difficult or impossible to recycle. The layers are usually formed from arc-shaped sheets cut separately from blanks, so that they do not make the most efficient use of paper. Furthermore, the many manufacturing steps required make them too expensive to market. As a result, these cups have never achieved commercial success.